CONCORD, N.H. — A temporary increase in food stamps expires Oct. 31, meaning for millions of Americans, the benefits that help put food on the table won’t stretch as far as they have for the past four years. Food stamps, the Supplemental Nutrition Assistance Program, go to 47 million Americans a month, almost half of them children and teenagers. Starting in 2009, the federal stimulus pumped $45.2 billion into SNAP, increasing what would have been a monthly benefit of $588 a month to $668 for an average household of four. However, in November, that same family will start getting $632 a month, about a 5 percent cut. The monthly benefits, which go to 1 in 7 Americans, fluctuate based on factors including food prices, income and inflation. By The Associated Press